FIG. 1 depicts a rotor of an electric rotor of existing technology. The rotor has ten teeth. Slots are formed between adjacent teeth to accommodate a winding wound about the teeth. The winding comprises a number of coils (10-19) of wire wound about corresponding teeth. Each coil is wound about two of the teeth. The ends of each coil overlap with an end of each adjacent coil. FIG. 2 illustrates a graph of the distribution of the centers of gravity (O10-19) of the coils (10-19) of the rotor. The center of gravity (O10) of the first coil 10 is the nearest to the geometric center of the rotor, whereas the gravity center (O19) of the last coil 19 to be wound is furthest from the geometric center of the rotor, and the gravity center of the winding as a whole is shifted away from the geometric center of the rotor. Using this method of winding, the center of gravity of the winding deviates from the geometric center of the rotor, causing the rotor to be prone to deflection during the rotation and producing noise due to the unbalanced rotation.
Hence there is a desire for an electric DC motor which has a rotor wound with a winding with a center of gravity which is closer to the center of rotation of the rotor.